//! Extract is a feature to let you deserialize request to custom type.
//!
//! You can easily get data from multiple different data sources and assemble it into the type you want.
//! You can define a custom type first, then in `Handler` you can get the data like this:
//!
//! ```
//! # use salvo_core::prelude::*;
//! # use serde::{Deserialize, Serialize};
//! #[derive(Serialize, Deserialize, Extractible, Debug)]
//! // Get the data field value from the body by default.
//! #[extract(default_source(from = "body"))]
//! struct GoodMan<'a> {
//!     /// The id number is obtained from the request path parameter, and the data is automatically parsed as i64 type.
//!     #[extract(source(from = "param"))]
//!     id: i64,
//!     /// Reference types can be used to avoid memory copying.
//!     username: &'a str,
//!     first_name: String,
//!     last_name: String,
//! }
//!
//! #[handler]
//! async fn edit(req: &mut Request) {
//!     let good_man: GoodMan<'_> = req.extract().await.unwrap();
//! }
//! ```
//!
//! There is considerable flexibility in the definition of data types, and can even be resolved into nested structures as needed:
//!
//! ```
//! # use salvo_core::prelude::*;
//! # use serde::{Deserialize, Serialize};
//! #[derive(Serialize, Deserialize, Extractible, Debug)]
//! #[extract(default_source(from = "body", format = "json"))]
//! struct GoodMan<'a> {
//!     #[extract(source(from = "param"))]
//!     id: i64,
//!     #[extract(source(from = "query"))]
//!     username: &'a str,
//!     first_name: String,
//!     last_name: String,
//!     lovers: Vec<String>,
//!     /// The nested field is completely reparsed from Request.
//!     #[extract(source(from = "request"))]
//!     nested: Nested<'a>,
//! }
//!
//! #[derive(Serialize, Deserialize, Extractible, Debug)]
//! #[extract(default_source(from = "body", format = "json"))]
//! struct Nested<'a> {
//!     #[extract(source(from = "param"))]
//!     id: i64,
//!     #[extract(source(from = "query"))]
//!     username: &'a str,
//!     first_name: String,
//!     last_name: String,
//!     #[extract(rename = "lovers")]
//!     #[serde(default)]
//!     pets: Vec<String>,
//! }
//! ```
//!
//! View [full source code](https://github.com/salvo-rs/salvo/blob/main/examples/extract-nested/src/main.rs)

use std::marker::PhantomData;

use serde::Deserialize;

/// Metadata types.
pub mod metadata;
use crate::http::ParseError;
use crate::Request;
pub use metadata::Metadata;

/// If a type implements this trait, it will give a metadata, this will help request to extracts data to this type.
pub trait Extractible<'de>: Deserialize<'de> {
    /// Metadata for Extractible type.
    fn metadata() -> &'de Metadata;
}

/// Wrapper for Extractible type. `Handler`'s parameters does not allow two extractible types has lifetime, wrap these types with `LazyExtract`.
#[derive(Deserialize)]
pub struct LazyExtract<T> {
    #[serde(skip)]
    _inner: PhantomData<T>,
}

impl<'de, T: Extractible<'de>> Default for LazyExtract<T> {
    fn default() -> Self {
        Self::new()
    }
}

impl<'de, T: Extractible<'de>> LazyExtract<T> {
    /// Create a new `LazyExtract` instance.
    pub fn new() -> Self {
        LazyExtract {
            _inner: PhantomData::<T>,
        }
    }

    /// Get the inner type.
    pub async fn extract(self, req: &'de mut Request) -> Result<T, ParseError> {
        req.extract().await
    }
}
impl<'de, T> Extractible<'de> for LazyExtract<T>
where
    T: Extractible<'de>,
{
    fn metadata() -> &'de Metadata {
        T::metadata()
    }
}
